In general, the invention relates to the fields of hydrogels, drug delivery systems, wound healing, and reduction of pain and inflammation.
Corneal wounds caused by injury, disease, or surgery represent a serious medical condition that may lead to loss of sight. For example, persistent epithelial defects can lead to stromal melting, which causes serious visual dysfunction. Wound healing of corneal mucosal tissue has taken on increased importance with the advent of laser corrective surgery to re-establish normal vision for people who do not wish to wear contact lenses or spectacles. These laser surgical methods are used to correct vision for nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. The methods include laser in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK), and photo-refractive keratectomy (PRK).
LASIK refers to the use of a laser to reshape the cornea without invading the adjacent cell layers. During the LASIK procedure a microkeratome is used to separate the surface layers of the cornea and create a corneal flap (160–180 microns deep). This flap stays attached to the rest of the cornea and is folded back on one side to expose the stroma of the cornea. The laser delivers pulses of ultraviolet light onto the inner cornea (stroma). Each pulse removes a microscopic layer of the inner cornea to reshape the surface of the cornea. For nearsighted patients, the procedure flattens the cornea. For farsighted patients, the procedure increases the curvature of the cornea. For astigmatism, selected tissues are removed at certain angles to make the cornea more spherical in shape. After exposure to the laser is completed, the corneal flap is replaced where it bonds without the need for stitches. The anterior layers of the cornea (epithelium, Bowman's Layer) are largely preserved. Once the surgery is completed, the eye is left to heal normally with the exception of eye drops, which are used to prevent infection & swelling, with varying degrees of success. Following the surgery, patients are able to see clearly without depending on glasses or contacts.
During PRK, the surgeon removes the epithelium (the anterior layer of the cornea or Bowman's Layer), which is a thin layer of protective skin that covers the cornea. This layer can be removed with an excimer laser or a brush. During the procedure, the patient stares at a fixation light. In less than a minute, the laser removes the proper amount of tissue while it reshapes the surface of the cornea. The excimer laser delivers pulses of ultraviolet light into the cornea. This exposure to laser radiation reduces or eliminates nearsightedness by flattening the central cornea and relocating the focal point of the lens onto the retina rather than in front of it, which produces sharper vision. Following surgery, a bandage contact lens is placed on the eye for 2–3 days. Because the epithelium was removed, patients may experience blurry vision for three to five days. Eye drops and the contact lens are effective in reducing postoperative discomfort. The purpose of the contact lens given to PRK patients post-surgically is to protect the leading edge of the corneal epithelium that is regenerating along the surface of the eye, post-surgery. As patients blink, the newer leading edge of the epithelium may be removed. As a result, recovery takes longer and there is an increased risk of infection.
LASEK is similar to PRK but the epithelium is detached by using an alcohol solution that weakens the epithelium and allows it to fold back into a flap. A laser is then used to re-shape the cornea and correct vision acuity.
All three procedures can result in corneal epithelial defects, and inflammation and infection may also occur. These complications can lead to acuity regression, pain, or other adverse effects. Corneal defects from injury or other types of surgery, such as corneal transplants, may also results in these undesirable outcomes. Wound healing is thus of critical importance for the outcome of surgery. There exists a need, therefore, for devices and treatments that promote healing of corneal wounds.